Field of the Invention
The present invention refers to an optical cable, preferably for aerial applications. However it can also be used underground and has high mechanical and heat performance properties because of its construction.
Optical cables in aerial networks are installed in electrical power distribution networks of medium and low tension or in its own pole line, in urban and rural areas. In rural areas, accidents frequently occur with optical cables, due to fire caused by natural or forced burning of local vegetation and also caused by hunter's shots.
Other important aspects of aerial optical cables are the installation conditions, i.e., maximum distance between poles and sag, climatic conditions, etc., which must be seriously taken into account.
Therefore, an object in the design of aerial optical cables is to meet the above mentioned installation conditions, as well as, when necessary, to withstand heat conditions caused by the above-mentioned fires or the mechanical damage caused by hunter's guns, without damaging the fibers or altering their optical characteristics.
In the market there are different types of totally dielectric aerial optical cables, which have several advantages over the traditional solutions of metallically sheathed cables, which use corrugated or smooth aluminium or steel tapes. However, principally from the resistance point of view against fires and gun shots, the dielectric solutions exhibit a low performance and complexity in the production process.
Furthermore, the construction of totally dielectric aerial optical cables, to be installed with large spans, requires a great number of textile pull elements so as to resist the mechanical stress in the climatic and more critical installation conditions (e.g. maximum wind force, minimum temperature, etc.). This excessive number of textile elements, in addition to presenting difficulties in the cable's manufacturing cycle, increases the unit weight as well as the cable's outside diameter, making its dimensions more critical.
An alternative, having high efficiency and proven through various practical applications, is the use of lightning conductors optical cables (OPGW). These OPGW cables have exceptional optical and mechanical characteristics, since they have around their dielectric nucleus, where the optical fibers are housed, an aluminium tube and surrounding it one or more layers of metallic wires.
These cables are preferably indicated for new aerial installations in power transmission lines or replacing conventional lightning conductor cable, offering one of the highest security coefficients against accidents caused by different factors, including fire and gun shot.
These cables also have been used in distribution networks or their own pole lines, to take advantages of their exceptional optical and mechanical features. However, for these installations, this alternative is not always the best solution from the economical point of view.